The present invention relates to a color-image sensing apparatus which performs color-imaging according to a frame-sequential system.
As a prior art example of such a color-image sensing apparatus, there is an electronic endoscope in which a solid-state image sensing device, such as a CCD, is contained in the distal end of its insertion section. Usually, endoscopes are used for observing the inside of the body cavity or narrow tubular members, which are pitch-dark or very dark. Therefore, use of an illumination light from a light source unit is essential to the observation. Thus, in a frame-sequential electronic endoscope, a rotary filter, having red, green, and blue color components, is located in front of a lamp. As the filter makes one revolution, an illumination light, which is emitted from a light source unit and applied to a light guide of the endoscope, is colored red, green, and blue, in succession. Then, images of the individual color components are stored into their corresponding frame memories. After the images of the three color components are stored in the frame memories, they are read out simultaneously, and displayed as a resultant full-color image on a CRT monitor.
Thus, according to the frame-sequential system, three color-component images are synthesized into one full-color image. In producing a still picture of a quickly moving object, therefore, the three component images are subject to a shearing in color, and cannot provide a high-quality picture.
Such an awkward situation may possibly be avoided by increasing the rotating speed of the rotary filter to pickup the three color-component images in a shorter period of time. If this is done, however, photographing periods for the individual component images will inevitably become too short to ensure a satisfactory quantity of light for the illumination.
In a light source unit having a flashing lamp, such as a stroboscope or a lamp capable of intermittent lighting (pulse lighting), it is necessary to use a diaphragm mechanism to control exposure since the amount of flash light is constant. The diaphragm mechanism makes the light source unit complicated in structure.
These circumstances are not limited to electronic endoscopes, and hold true of any color-image sensing apparatuses of a frame-sequential system.